The disclosed technology relates to lubricants for internal combustion engine, particularly those fueled with biodiesel fuels.
Biodiesel is a general term for fuel-grade materials derived from natural sources such as vegetable oils. They are often fatty acid methyl esters (“FAME”) such as rapeseed methyl ester (“RME”) or soya methyl ester (“SME”). Biodiesel fuels are becoming more prevalent for fueling of diesel engines. The increased use of diesel passenger vehicles in Europe and elsewhere is in part a cause of this increase. Current European diesel standard (EN 590) allows for 5% biodiesel component to be incorporated into fuels, which will soon rise to 7%, with indications that 10% biodiesel content will be introduced by 2012.
Simultaneously, there is continued pressure for reducing particulate matter emissions from diesel engines. Euro 5 requirements, scheduled for implementation in 2009, require reduction in particulate matter to 0.05 g/km. Such levels can only be attained, practically, by use of a diesel particulate filter. These filters require regeneration once they are full of soot, and this is typically achieved by increasing the filter temperature to burn off the soot. The temperature increase is often achieved by post-injection of fuel into the engine cylinder.
However, post-injection of fuel can have the undesirable effect of fuel-dilution of the engine lubricant, as more cylinder wall wetting by the fuel allows more fuel to migrate to and accumulate in the lubricant sump. Biodiesel components are typically less volatile than conventional mineral diesel fuel, and thus concentration of such components in the sump is exacerbated. In fact, use of biodiesel fuel (B05, i.e., containing 5% ester) along with post-injection may result in 40% fuel dilution of the lubricant, and the biodiesel component may account for 50% of the diluent. These high levels of biodiesel in the oil may lead to increased oxidation and deposit formation associated with the lubricant.
U.S. Patent Publication 2008/0182768, Devlin et al, Jul. 31, 2008, discloses a lubricant composition for biodiesel fuel engine applications, containing an oil of lubricating viscosity and a highly grafted, multi-functional olefin copolymer. The lubricating oil may contain a conventional dispersant/inhibitor package, which may contain a detergent such as oil soluble neutral and overbased sulfonates and phenates, among others.
U.S. Patent Publication 2009/0111720, Boffa, Apr. 30, 2009, discloses lubricating oil compositions contaminated with a biodiesel fuel, comprising a base oil of lubricating viscosity an a diarylamine compound. It further comprises at least one additive which may be (among others) detergents. Suitable metal detergents include phenates and sulfonates, among others. Generally the amount of the detergent is from about 0.001 wt. % to about 5 wt %. In an example, a base-line comparison is prepared containing, among other materials, 0.24 wt. % actives of an overbased magnesium sulfonate and 0.65 wt. % actives of an overbased calcium phenate detergent.
U.S. Patent Publication 2009/0111721, Boffa, Apr. 30, 2009, discloses lubricating oil compositions comprising a base oil, a biodiesel fuel, and a detergent. The detergent can be a metal phenate detergent such as alkaline metal phenates. An additional additive or modifier may also be present, including detergents. Suitable metal detergents include phenates and sulfonates. In an example, a baseline formulation contains 0.18 wt. % actives of a low overbased calcium sulfonate detergent.
PCT Publication WO 2009/013275, Jan. 29, 2009, discloses lubricating composition for use in diesel engines compatible with biofuel, containing certain antioxidants. The lubricant may also contain an additives package containing detergent.
The disclosed technology provides a lubricant composition suitable for sump lubricated engines fueled by a liquid fuel which includes a biodiesel component, which exhibits improved oxidation resistance and/or reduced deposit formation in lubricants which contain a portion of the biodiesel component. This is accomplished by the presence of the described sulfonate material.